Projectile propelling apparatus for use in high temperature environment



Feb. 22, 1966 A. A. VENGHIATTIS PROJECTILE PROPELLING APPARATUS FOR USE IN HIGH TEMPERATURE ENVIRONMENT Filed July 2, 1962 as X FIGI

INVENTOR. ALEXIS A. VENGHIATTIS QMW HIS ATTORNEY United States Patent Oil ice 3,236,317 Patented Feb. 22, 1956 3,236,317 PRGJECTILE PROPELLIN G APPARATUS FGR USE IN HlGH TEMYERATURE ENVERDNMENT Alexis A. Venghiattis, Houston, Tex, assignor to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Filed July 2, 1962, Ser. No. 206,979 6 Claims. (Cl. 175-458) This invention relates to projectile propelling apparatus particularly adapted for use in high temperature environments, such as those found in oil wells, and to the method of operating such devices.

In the completion of oil and gas wells, it has long been customary to perforate the steel casing set in the well bore, the surrounding cement sheath and the adjacent earth formation in order to permit the fluids in the formation to flow into the well bore. At present, the two most widely used perforating devices are bullet guns and shaped charges. The selection of which of these types of perforators to use is frequently determined by the nature of the earth formation to be perforated but, apart from this, each type of perforator has advantages and disadvantages with respect to the other. The bullet perforator is somewhat cheaper to operate and has greater flexibility in perforation spacing because the individual bullets making up a gun assembly may be tired independently of one another whereas, at the present time, shaped charges can only be fired in volleys. On the other hand, the high temperatures encountered in very deep wells cause spontaneous ignition of the propellant charges used in bullet guns and result in their uncontrolled firing. Heretofore, bullet guns have utilized low explosive propellants, such as nitrocellulose, or mixtures of nitrocellulose and nitroglycerine (double base powders). High explosives, which are generally more temperature stable, were considered unsuitable for bullet guns since detonation of these materials would destroy or damage the gun body. For this reason, it has been impossible to use bullet guns in high temperature wells and the use of shaped charges has been required. This is sometimes a disadvantage because of the aforementioned considerations of price and lack of flexibility of perforation spacing and also because certain earth formations are more effectively perforated by bul lets than by shaped charges.

It has been found that even when a high explosive is deflagrated, rather than detonated, the rate of combustion may be so high as to cause substantial damage to the gun. This damage is not the sudden splitting of the gun body, as is caused by detonation, but rather gradual enlargement of openings and displacement of parts due to successive applications of high stresses. This attritive damage materially shortens the life of a perforaior. Because the rate of combustion of a deflagrated high explosive is directly proportional to the initial temperature of the explosion, the danger of gun damage of this type is particularly great in hot wells where the use of a high explosive propellant would be desirable because of its temperature stability.

It is an object of this invention to provide a projectile propelling gun, such as a bullet gun, that is capable of controlled operation in high temperature environments, that is, in the order of 400 F.

It is another object of this invention to provide a projectile propelling gun for use in high temperature oil wells that is capable of being used a great many times without substantial deformation or damage.

It is yet another object of this invention to provide an explosive material that is both stable at relatively high temperature and also capable of controlled deflagration.

It is a further object of the invention to provide a method of operating a projectile propelling gun, such as a perforator or a core sampler, in high temperature environments without damage to such devices.

In general, these and other objects of the invention are attained by providing a projectile propelling gun including a firing chamber, a body of secondary high explosive, preferably containing from about 10% to about 20% by weight of inert material, in the firing chamber for propelling a projectile and further providing means for actuating the explosive in a dellagrating rather than a detonating manner. Such actuating means preferably comprise a body of low explosive such as black powder.

In this specification and in the appended claims, the terms primary high explosive," secondary high explosive, low explosive, defiagrate and detonate are used in accordance with the usage of American Chemical Society Monograph 139, The Science of High Explosives by Melvin A. Cook, published by Reinhold Publishing Corporation, 1958. See particularly pages 1-4, inclusive.

In the accompanying drawings:

FIG. 1 is a view in elevation of a typical Well perforating gun embodying features of the present invention, and

FIG. 2 is a partial transverse section taken on the line 22 of FIG. 1.

FIGS. 1 and 2 illustrate, in somewhat simplified form, a perforator of the type described and shown in US. Patent 2,953,971 to Forrest V. Porter, issued September 27, 1960. Reference may be had to that patent for a more complete description of those details of the structure of the device which are not a part of this invention. In FIG. 1, the numeral 10 indicates a gun assembly generally, and the numeral 12, the gun body. The gun comprises a steel cylindrical assembly which is adapted to be lowered into a well bore by conductor cable 11, containing an insulating conductor or conductors, through which the firing of the units may be controlled. As indicated in FIG. 1, between the conductor cable 1 1 and the body 12 of the gun there are provided a cable socket 13 and various interconnecting subs. One such sub, shown at 14, contains suitable fire control means, as indicated in dotted lines at 15, with respect to which this invention is not specifically concerned.

Referring more particularly to FIG. 2, the gun body 12 comprises a generally elongated, substantially solid, steel cylinder of sufiicient strength and solidity to withstand explosive forces of the firing of the gun charges. Laterally directed gun units are mounted in the cylindrical gun body at longitudinally spaced intervals and preferably in a spiral arrangement, as shown in FIG. 1. Each unit comprises an internally threaded, laterally directed barrel opening 16 which receives the threaded barrel member 17. The barrel member 17 is formed with a con centric barrel bore 22 the outer end of which is sealed with a disc 24 in any suitable manner well known in the art, and may be formed of any suitable material, such as brass or steel. In operation, when the propellant charge is ignited and the bullet fired, the seal 24 is ejected either as a unit or in fragments and forms no obstacle to the discharge of the bullet.

The well casing or formation piercing projectile or bullet is indicated at 26 and preferably comprises a forward piercing nose portion 27 of substantially conical or ogival form, and a body or rearward shank portion 28, preferably of uniform diameter, extending from the nose portion 27 to a transverse rear end or butt 29. The bullet 26 is mounted through a central opening formed in a sealing plate or diaphragm 30, and also through a frustoconical restraining annulus 31, both of which engage the cylindrical midsection of the bullet approximately midway between the forward end of the nose portion 27 and the butt 29. While the plate 30 and the annulus 31 are shown as separate parts, they may be integral. The opening through both plate 30 and annulus 31 are preferably such as to form a fit of controlled tightness upon the bullet 26. The annulus 31 and the plate 30 form restraining means from which the bullet is dislodged only upon the building up of sufiicient pressure within the firing chamber by deflagration of the propellant charge.

A cylindrical firing chamber is shown at 40, formed by a bore 41 of inside diameter reduced relative to that of the threaded barrel opening 16 but uniform throughout its length and extending concentrically inward from the innermost end of the barrel opening 16. The firing charge within firing chamber 40 is made up of secondary high explosive body 45 in consolidated or pelletized tubular form and having an opening or passage 46 extending centrally therethrough from end to end. The body 45 is shown as surrounded by a sleeve or shell 47 which is more fully described in relation to the other parts of the structure in the aforementioned Porter patent.

In the embodiment of the invention described, actuation of the body 45 is accomplished by means of igniter 44 which is preferably a cup-like head member, containing a combustible low explosive powder such as black powder and an electrical resistance element therein (not shown). Construction of this particular type of igniter is disclosed in US. Patent 2,649,736 to Robert A. Phillips and the actuation of such igniter is accomplished by means described and illustrated in the aforementioned Porter patent.

In accordance with this invention the body 45 comprises a secondary high explosive, for example, trimethylenetrinitramine, commonly referred to as cyclonite or RDX. Heretofore, bullet perforating guns have uniformly utilized a low explosive such as double base powder. The use of the latter type of explosive prevented bullet perforators from being operated at temperatures much in excess of 300 F. This is because such low or deflagrating explosives ignite spontaneously when maintained at temperatures above 300 F. for the period of time that a perforating assembly is normally in the oil well. Cyclonite, on the other hand, is capable of withstanding temperatures on the order of 350 F. for 24 hours Without self-ignition and to withstand temperatures as high as 390 F. for the length of time normally required to run the perforator in the high temperature portion of an oil well.

An important feature of the invention is the use of a low explosive or deflagrating initiator in combination with a secondary high explosive of the type conventionally detonated. It is important to prevent detonation of the explosive body 45 otherwise the gun body 12 will be split and the tool ruined. In accordance with this invention, it has been found that secondary high explosives may be ignited in a deflagrating rather than a detonating manner by use of a low explosive as an initiator. Low explosives, such as black powder or smokeless powder (which themselves are defiagrated by heat) have been found to initiate deflagration of secondary high explosives such as cyclonite, whereas the use of conventional detonators or boosters of the so-called primary high explosive type (lead azide, mercury fulminate etc.) would cause the same secondary high explosive to detonate.

Although black powder is a preferred actuating means for this invention, it will be understood that other conventional low explosives may be employed, for example, a commercially available mixture of boron chromate and barium chromate. Primary high explosives of the type ignited by impact, such as lead aZide, should not be used as initiators because they will cause detonation of the secondary high explosive body and damage or destroy the gun.

The mode of actuation of the secondary high explosive is determinative of whether its combustion will initially follow the deflagrating rather than the detonating course. Because detonation of body 45 must be avoided to prevent damage to the perforating tool, it is also important to keep the ambient pressure around the tool, it is also important to keep the ambient pressure around the explosive body from reaching a level at which there is a transition from explosive deflagration to detonation. For cyclonite this pressure is in the order of 20,000 kilograms per square centimeter. It has been found that for most secondary high explosives useful as propellants excessive pressure build-up is avoided by fitting the bullet 26 into the restraining members 30 and 31 by means of a tight press fit. As explained in the aforementioned Porter patent, it is necessary to restrain the movement of the bullet 26 until combustion of the propellant explosive has been substantially completed so that its propelling force can be efficiently utilized and sufiicient kinetic energy supplied to the projectile to enable it to accomplish the required perforation. It has been found that the tight press fit which accomplishes this desirable result also permits movement of the bullet 26 from the firing chamber before the pressure therein can be built up to a value at which transition from deflagration to detonation takes place.

It will be appreciated that other secondary high explosives besides cyclonite may be used in this invention and that such explosives have different critical pressures at which detonation occurs. For such other detonating explosives, obviously, different restraining forces on the bullet 26 may be required. It has been found, however, that for most secondary high explosives useful in well perforators the restraining force (on the order of 1,000 pounds) provided by a tight press fit of bullet 26 (which has a shank diameter on the order of one-half inch) into members 30 and 31 provides suitable release means for preventing the pressure in firing chamber 40 from building up to the point at which initial deflagration becomes detonation.

Although deflagration of explosive body 45 avoids sudden destruction of the gun as by splitting the body 12, it has been found that deflagration at too high a combustion rate may produce shock forces that cause deformation and enlargement of the barrel member 17 and other parts of the gun. This causes the performance of the gun to deteriorate substantially after only a few charges have been fired and thus shortens the useful life of the tool. In order to reduce the rate of deflagration of body 45 so that such gradual damage is minimized, a preferred embodiment of this invention includes the incorporation of a selected amount of inert material, such as talc, into explosive body 45. Where cyclonite is used as the low explosive, from about 10% to about 20% by weight of body 45 is inert material with a preferred composition being about by weight cyclonite and about 15% by weight talc.

The inert component of the mixture is preferably in the form of a very finely divided powder having an average particle size smaller than that of the explosive substance. This is to permit particles of the inert material to coat the explosive particles and delay the transmission of flame between them. Although talc is the preferred inert component of the composition of this invention, any other non-combustible material that will suitably delay flame transmission may also be used.

Although this invention has been described in connection with bullet perforating guns, it will be recognized that it has applications in connection with other projectile propelling tools such as core samplers used in high temperature environments such as found within oil wells. Other applications, as well as the use of secondary high explosives, low explosives, and inert materials other than those specifically enumerated will occur to those skilled in the art and are within the purview of this invention.

I claim:

1. In a projectile propelling gun for use in a high temperature environment, formed of a gun body, means forming a firing charge chamber in the gun body, means defining a barrel bore in communication with the firing charge chamber, a projectile slidably fitted in the barrel bore and a firing charge in the firing chamber, the improvement comprising the firing charge being formed of:

a body in which the propellant is exclusively secondary high explosive; and

igniting means developing sufficient energy to deflagrate the firing charge but insufiicient energy to detonate it.

2. In a projectile propelling gun for use in a high temperature environment, formed of a gun body, means forming a firing charge chamber in the gun body, means defining a barrel bore in communication with the firing charge chamber, a projectile slidably fitted in the barrel bore and a firing charge in the firing chamber, the improvement comprising the firing charge being formed of a body in which the propellant is exclusively secondary high explosive;

igniting means developing suificient energy to deflagrate the firing charge but insutficient energy to detonate it; and

means for maintaining the ambient pressure around said firing charge below that at which there is transition from defiagration to detonation of said firing charge.

3. The combination according to claim 2 wherein said secondary high explosive is cyclotrimethylenetrinitramine.

4. The combination according to claim 2 wherein said means for deflagrating includes black powder.

5. The combination according to claim 2 wherein inert material is interspersed with the secondary explosive in the firing charge to delay the flame transmission between the grains of the secondary explosive.

6. In a projectile propelling gun for use in a high temperature environment, the combination comprising:

means forming a firing chamber in said gun;

a body in which the propellant is comprised exclusively of secondary high explosive in said chamber; means for defiagrating said body; a projectile positioned as a closure for said chamber;

and restraining means holding said projectile against initial movement from its closure position, said restraining means adapted to permit movement of said projectile when the pressure within said chamber has reached a level less than at which there is transition from defiagration to detonation of said body.

References Cited by the Examiner UNITED STATES PATENTS 2,565,788 8/1951 Tow 166-554 2,593,620 4/1952 Spencer 166-554 2,638,323 6/1953 Bannon -3 2,649,736 8/1953 Phillips 166-555 X 2,697,325 12/ 1954 Spaulding 102-49 X 2,718,264 9/1955 Allen et al. 166-35 X 2,724,237 11/1955 Hickman 102-49 X 2,916,996 12/1959 Coffee 102-98 2,942,547 6/1960 Rabern et al 102-98 X 2,944,486 7/1960 Jasse 102-49 2,953,971 9/1960 Porter 166-55 X 3,000,718 9/1961 Campbell et al. 149-19 3,012,609 12/1961 Toelke 166-55.4 3,093,521 6/1963 Breza 149-19 CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner. 

1. IN A PROJECTILE PROPELLING GUN FOR USE IN A HIGH TEMPERATURE ENVIRONMENT, FORMED OF A GUN BODY, MEANS FORMING A FIRING CHARGE CHAMBER IN THE GUN BODY, MEANS DEFINING A BARREL BORE IN COMMUNICATION WITH THE FIRING CHARGE CHAMBER, A PROJECTILE SLIDABLY FITTED IN THE BARREL BORE AND A FIRING CHARGE IN THE FIRING CHAMBER, THE IMPROVEMENT COMPRISING THE FIRING CHARGE BEING FORMED OF: A BODY IN WHICH THE PROPELLANT IS EXCLUSIVELY SECONDARY HIGH EXPLOSIVE; AND IGNITING MEANS DEVELOPING SUFFICIENT ENERGY TO DEFLAGRATE THE FIRING CHARGE BUT SUFFICIENT ENERGY TO DETONATE IT. 